The criteria for the next Republican debate could shrink the debate stage to just six candidates, potentially pushing John Kasich, Carly Fiorina and Rand Paul out of the main event and into the undercard debate, POLITICO has learned.

According to debate criteria that were to be announced Tuesday, host Fox Business Network will consider both early-state and national poll results in deciding which candidates make the prime-time forum. That main debate will feature candidates who place in the top six nationally, based on an average of the five most recent national polls recognized by Fox News, or place within the top five based on an average of the five most recent Iowa or New Hampshire state polls recognized by the network.

Story Continued Below

The polls being considered must be released prior to 6 p.m. Eastern time on Monday, Jan. 11, and be conducted by major nationally and state recognized organizations that use standard methodological techniques, such as live interviewers and random digit-dial sampling techniques using both landlines and cellphones.

There's no limit on the number of candidates on the main stage. But according to POLITICO calculations based on only the national polling available as of Tuesday, the prime-time debate stage would include Donald Trump, Sen. Ted Cruz, Sen. Marco Rubio, retired neurosurgeon Ben Carson, former Gov. Jeb Bush and Gov. Chris Christie. The early state polling wouldn't change the lineup as of Tuesday, according to POLITICO calculations of Iowa and New Hampshire polls.

To qualify for the earlier undercard debate, candidates must register at least 1 percent in one of the five most recent national polls, as recognized by Fox News.

According to polling released as of Tuesday, the undercard debate stage would include Sen. Paul, Gov. Kasich, Fiorina, former Gov. Mike Huckabee, former Sen. Rick Santorum and former Gov. George Pataki.

The networks are still struggling to accommodate the unwieldy GOP field, which has been winnowed to 13 but still represents a sprawling contest. Controversy has swirled around the lineup for multiple debates, with criteria changing twice to get Fiorina bumped up to the main event during the second debate and Paul clinging to the prime-time stage of the most recent GOP debate despite technically not having the right numbers.

The Fox Business debate will be held at the North Charleston Coliseum and Performing Arts Center in North Charleston, South Carolina.